Ensure that the target you are reading has no defects in the patches, and that it is properly aligned in the pathfinder guide.

Close and restart the software application.

Perform a calibration on the instrument (see related support articles links in the left hand column for calibration instructions).

Optics need cleaning (see related support articles links in the left hand column for optics cleaning instructions).

Reset the instrument (see related support articles links in the left hand column for reset instructions).